DESCRIPTION The long-term objectives of this project are to determine the mechanism(s) whereby GCs suppress male reproductive function. GCs have been previously show to have actions directly at the level of the testis, and to inhibit the expression of genes which encode testosterone biosynthetic enzymes. GCs have also been shown to control processes of cell proliferation and apoptosis in other cell types. The first and second specific aims of the proposal are to examine the effects of GCs administered either in vivo or in vitro on Leydig cell mitosis and apoptosis. The third specific aim of the proposal is to determine the level of c-jun expression in Leydig cells after treatment with GCs in vivo and in vitro. In all specific aims, cells will be prepared from rats of 3 different ages which span key development stages of the Leydig cell maturation, and will be treated with levels of GC which reflect either the normal milieu or that which would be expected under conditions of stress.